Wavelength division multiplexed optical communication systems are characterized by multiple channel output over single optical fibers. Conventional systems use a single light source for each channel, wherein each light source is configured to emit at the particular frequency that has been uniquely assigned to it among the multiple frequencies emitted by the system. The emission frequency of each light source is precisely controlled. A typical system will employ several (e.g., 5-100) of these light sources emitting at precisely controlled frequencies. Standards exist which govern the desired spacing between frequencies in such systems, and spacing values of 25, 50, or 100 GHz are typical values being discussed for current and emerging systems.
Currently, these conventional sources are DFB lasers emitting at fixed and precisely controlled wavelengths. In this scenario, a discrete laser is required for each transmission channel. Due to the large number of channels desired, a large number of discrete lasers is required, and the system becomes large and complex, and has a large number of components subject to failure at any one time. Because of the possibility of failure, a system with a large number of lasers will also require a large number of spare lasers for replacement.
There is at present a desire to partially solve this problem by using sources that are tunable, such that a single laser source may be used to emit at multiple frequencies, allowing some reduced number of spare lasers to be used to cover the frequency span of interest. A large, albeit reduced, number of laser sources are still used in this technique, although the number may be made to be more manageable with this approach. In addition, this approach does not solve the problem of increased laser count as channel count increases.
U.S. Pat. No. 5,347,525 describes an arrangement wherein a master oscillator emits at multiple frequencies as a multimode laser. A modulation/amplification section then amplifies and individually modulates the cavity modes before multiplexing the modes and coupling them to a communication system. The master oscillator is selected as a diode pumped solid state laser (DPSSL) in the ""525 patent due partly because the linewidths and number of modes available with conventional diode lasers doesn""t allow for multimode optical communication over a sufficiently high number of resolved frequencies. In addition, the master oscillator/modulator-amplifier design of the ""525 patent entails an extra component adding to the complexity of the arrangement.
Fiedler and Ebeling disclose a vertical cavity surface emitting laser (VCSEL) and fiber resonator with a dielectric mirror at IEEE Journal of Selected Topics in Quantum Electronics, Vol. 1, no. 2, pp. 442-450 (June 1995). Multiple closely-spaced ( less than 1 GHz) optical communication modes are described as being achieved with this system. The cavity length is around 18.2 cm mostly being the length of the single mode optical fiber that is part of the resonator. Required coupling of the VCSEL to the fiber optic and transmission along the intra-cavity fiber optic cable results in a loss of efficiency and problems with noise and resolution.
In view of the above, it is an object of the invention to provide an efficient multi-channel DWDM transmitter.
In accord with the above object, a multi-channel light source for use with a wavelength division multiplexed optical communication system includes a modified vertical cavity surface emitting laser (VCSEL) including a gain region and a resonator reflector layer at a first end for coupling with an optical fiber. A pumping source excites a gain region of the laser. An external cavity couples at a second end of the modified VCSEL and has a mirrored end for forming a resonant cavity with the resonator reflector layer permitting the light source to produce a multi-channel optical signal. The modified VCSEL has a cavity length that is substantially extended compared with a conventional VCSEL which has a resonant cavity formed within a layer structure of the conventional VCSEL.
In further accord with the above object, a multi-channel light source for use with a wavelength division multiplexed optical communication system is provided including, a modified vertical cavity surface emitting laser (VCSEL) including a gain region and a resonator reflector layer at a first end for coupling with an optical transmission medium, a pumping source for exciting a gain region of the laser, an oscillating signal generator for providing active mode-locking in the gain region of the laser, and an external cavity coupling at a second end of the modified VCSEL and having a mirrored end for forming a resonant cavity with the resonator reflector layer and permitting the light source to produce a multi-channel optical signal, wherein the modified VCSEL has a cavity length that is substantially extended compared with a conventional VCSEL which has a resonant cavity formed within a layer structure of the conventional VCSEL.
In further accord with the above object, a multi-channel light source for use with a wavelength division multiplexed optical communication system is provided including a modified vertical cavity surface emitting laser (VCSEL) including a gain region and a resonator reflector layer at a first end for coupling with an optical transmission medium, a pumping source for exciting a gain region of the laser, a saturable absorber for providing passive mode-locking in the gain region of the laser, and an external cavity coupling at a second end of the modified VCSEL and having a mirrored end for forming a resonant cavity with the resonator reflector layer and permitting the light source to produce a multi-channel optical signal, wherein the modified VCSEL has a cavity length that is substantially extended compared with a conventional VCSEL which has a resonant cavity formed within a layer structure of the conventional VCSEL.
In further accord with the above object, a multi-channel light source for use with a wavelength division multiplexed optical communication system is provided including a modified vertical cavity surface emitting laser (VCSEL) including a gain region and a resonator reflector layer at a first end for coupling with an optical transmission medium, a pumping source for exciting a gain region of the laser, a mode-locker for providing mode-locking in the gain region of the laser, and an external cavity coupling at a second end of the modified VCSEL and having a mirrored end for forming a resonant cavity with the resonator reflector layer and permitting the light source to produce a multi-channel optical signal, wherein the modified VCSEL has a cavity length that is substantially extended compared with a conventional VCSEL which has a resonant cavity formed within a layer structure of the conventional VCSEL.
In further accord with the above object, a multi-channel light source for use with a wavelength division multiplexed optical communication system is provided including a modified vertical cavity surface emitting laser (VCSEL) including a gain region and a resonator reflector layer at a first end for coupling with an optical transmission medium, a pumping source for exciting a gain region of the laser, a passive mode-locker means for providing passive mode-locking in the gain region of the laser, and an external cavity coupling at a second end of the modified VCSEL and having a mirrored end for forming a resonant cavity with the resonator reflector layer and permitting the light source to produce a multi-channel optical signal, wherein the modified VCSEL has a cavity length that is substantially extended compared with a conventional VCSEL which has a resonant cavity formed within a layer structure of the conventional VCSEL.
In further accord with the above object, a multi-channel light source for use with a wavelength division multiplexed optical communication system is provided including a modified vertical cavity surface emitting laser (VCSEL) including a gain region and a resonator reflector layer at a first end for coupling with an optical transmission medium, a pumping source for exciting a gain region of the laser, an active mode-locker for providing active mode-locking in the gain region of the laser, and an external cavity coupling at a second end of the modified VCSEL and having a mirrored end for forming a resonant cavity with the resonator reflector layer and permitting the light source to produce a multi-channel optical signal, wherein the modified VCSEL has a cavity length that is substantially extended compared with a conventional VCSEL which has a resonant cavity formed within a layer structure of the conventional VCSEL.